The invention discloses an engine and a braking mechanism thereof. The braking mechanism comprises a
cam shaft, a
tappet, a gas distribution mechanism, a first valve and a second valve, wherein the
tappet is driven by the
cam shaft; the
tappet is provided with a
piston cavity, an
oil supply pipeline and an oil leakage pipeline, the
oil supply pipeline and the oil leakage pipeline communicate with the
piston cavity, and a
piston is arranged in the piston cavity; the gas distribution mechanism is used for controlling an
exhaust valve to be opened or closed, and a braking gap is formed between the piston and the gas distribution mechanism; the first valve is used for controlling a braking oil duct to communicate with or separate from the
oil supply pipeline; and the second valve is used for controlling the oil leakage pipeline to communicate with or separate from the outside. When braking is needed, oil is supplied in the braking oil duct, the first valve is controlled to be opened, the second valve is opened, when the piston moves to eliminate the braking gap, the first valve resets, the piston cavity forms a sealed cavity, accordingly, a braking
cam drives the tappet to act, and the piston drives the gas distribution mechanism to act. Through the arrangement, the braking mechanism of the engine can be applicable to the under cam shaft, the space of a cylinder cover is not occupied, and arrangement is convenient.